A heavy-duty pivot bearing is provided in particular, which is preferably used under high radial loads such as centrifuges with considerably reduced friction.
Pivot bearings are used for bearing machine elements which are subjected to a rotational movement about a rotational axis and whose rotational angles do not have a full rotation of 360°. This leads to an oscillating motion about a rotational axis with a more or less constant pivoting angle and an uneven rotational speed between zero and a positive and negative maximum value.
Plain bearings are not especially suitable for such working conditions, because it is hardly possible to build up a hydrodynamic lubricating film as a result of the pivoting movement and the uneven relative speeds between the bearing bolt and the bearing hole. This leads to increased frictional effects and respectively higher wear and tear and low operational lifespan. An acceleration directed radially to the outside is additionally produced in centrifuges (centrifugal acceleration), which leads to the consequence that lubricants will flow together in cylindrical bearing holes in the boundary region of the bearing hole which is farthest away from the center of the rotation and will be conveyed out of the bearing hole in the axial direction in the case of a lack of a suitable bearing seal and will be ejected radially to the outside from the edge of the bearing hole by centrifugal acceleration. This leads to the reduced or hardly provided hydrodynamic lubricating film as a disadvantage in addition to the increased escape of lubricant from the bearing hole and the reduced remaining lubricant volume in the plain bearing.
Rolling bearings usually have a higher weight in comparison to plain bearings (made of plastic) and show an unfavorable distribution of lubricant in the case of high centrifugal accelerations. This promotes increased wear and tear. Within the group of the rolling bearings, needle-roller bearings show the most advantageous conditions (weight, friction, . . . ) for such applications. In the case of such rolling bearings, cylindrical rollers with a rolling body diameter which is smaller in comparison with the bearing diameter are rolled off between the running surface of the outer ring and the inner ring (mostly the bearing bolt). Bearing friction is formed in this case by the rolling friction of the rolling body and the mean radius of the running surfaces of the outer ring and the inner ring. Rolling bearings show lower friction in comparison to plain bearings.
Furthermore, flexible pivot bearings on the basis of elastically deformable thin-walled membranes made of plastic or metal arranged in a crosswise manner are known. Pivot bearings are described in U.S. Pat. No. 3,807,029 A (Troeger H., 1974), U.S. Pat. No. 3,811,665 A (Selig F., 1974), U.S. Pat. No. 3,813,089 A (Troger H., 1974) and U.S. Pat. No. 3,825,992 A (Troeger H., 1974) whose fundamental principle is based on spring elements arranged in a crosswise manner, wherein a cylindrical middle body is inserted into the bearing hole in a twist-proof fashion and a second cylindrical body, which is twistably arranged in relation to the first cylindrical body, is connected to the machine element to be mounted. This produces a one-sided pivot bearing. In a second embodiment, two cylindrical hollow shafts which are rigidly connected to each other are connected by means of crosswise arranged membranes in relation to the middle body inserted in a twist-proof fashion into the bearing hole in such a way that a torque or a rotational motion can be transmitted from one lateral part to the other. As a result, a rotational movement can be transmitted by the middle body from one side to the opposite side. Such pivot bearings operate in a friction-free manner, but come with the disadvantage that only relatively low radial forces can be absorbed and only low pivoting angles can be carried out. Typical maximum pivoting angles lie in the range of approximately +/−30° (in the case of very low radial loads) and pivoting angles of only a few degrees can be carried out under higher loads. For this reason, such elastic pivot bearings are used only where very low radial forces occur such as in storage drives of computers, measuring devices and the like. A further elastic pivot bearing is known from U.S. Pat. No. 5,505,555 A (Van Kann Frank J; Buckingham Michael J, 1996), which also shows the aforementioned limitations and is therefore only used in special measuring appliances such as acceleration sensors for example.
Great Britain Patent Publication No. GB 146,119 A describes a joint arrangement in which tensile forces are transmitted via profiled surfaces. In the case of pressure forces, the joint arrangement acts in the manner of a plain bearing with respective disadvantages.